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Re: [Phys-l] homemade spacecraft!

I confess to having left the 'lifting power' comparison as a bit of a troll.
Yes H2 is only 8% more effective than He but the fact remains that He is a limited resource that has better uses. And Helium released into the atmosphere does irrecoverably escape into space.

The price of H2 must be quite a bit cheaper as well.

I'm still looking for youtube or such info on a straight unconfined H2 explosion.

I see fireballs from H2 bubbles.

At 5:37 PM -0700 10/19/10, M. Horton wrote:
"I'm surprised at how many groups are still using He (a VERY limited and
nonrenewable resource) instead of the more buoyant H2 alternative."

Chuck, it sounds like you creeped up on, but didn't quite directly state a
very common misconception about the lifting power of hydrogen and helium.
Many people think that because hydrogen has half the mass (and therefore
half the density) of helium, that it will have twice the lifting power. But
that's not how lifting power (or buoyant force) works.

The lifting power of a gas confined inside of a balloon is the difference
between the mass of the gas and the mass of an equal volume of air (minus
the mass of the balloon). So, if we assume exactly a 22.4L balloon at
standard temperature and pressure (i.e. one mole of gas), hydrogen has a
mass of 2.0 grams, helium has a mass of 4.0 grams, and air (approximately)
28.8 grams. So the lifting power of a hydrogen-filled balloon of this size
would be 26.8 grams and the lifting power of a helium-filled balloon would
be 24.8 grams. That's only an 8% increase. It's probably not worth the
additional cost and danger. A 10% larger helium balloon would be far
cheaper and safer.

I can't comment on the renewability. I doubt that it really went out of the
atmosphere, it would have exploded long before that. So, the helium is
probably still in the atmosphere somewhere.

I have an episode of my Science Misconception Podcast on this topic at


----- Original Message -----
From: "chuck britton" <>
To: "Forum for Physics Educators" <>;
Sent: Tuesday, October 19, 2010 12:30 PM
Subject: Re: [Phys-l] homemade spacecraft!

As someone else has already noted - there's a lot of this going on these
FAA regs allow for lightweight packages with no rigamarole (sp?)

I'm surprised at how many groups are still using He (a VERY limited
and nonrenewable resource) instead of the more buoyant H2 alternative.
> And the H2 adds even MORE excitement to an already exciting adventure ;-)